Aluminum Al Arsenic As Boron B Bromin Br Calcium Ca Carbon C Chlorin Cl Chromium Cr Copper Cu Fluorin F Gold Au Hydrogen H Iodin I Iron Fe Lead Pb Magnesium Mg Mercury Hg Nickel Ni Nitrogen N Oxygen O Phosphorus P Platinum Pt Potassium K Silicon Si Silver Ag Sodium Na Sulfur S Tin Sn Zinc Zn AIR AND OXYGEN [Sidenote: Composition of air] AIR--The air consists chiefly of two substances, only one of which can keep up the process of burning. This substance is known as oxygen. The other, in which nothing can burn, is known as nitrogen. Besides these the air contains smaller quantities of other substances, particularly water vapor, carbonic acid (carbon dioxid), ammonia, and carburetted hydrogen. [Sidenote: Distribution of oxygen] OXYGEN--Oxygen is the most common element in nature. It forms between forty and fifty per cent of the solid crust of the earth, eight-ninths of all the water on the globe, and one-fifth of all the air around the globe. We have oxygen around us in great abundance, but it is mixed with nitrogen, and it is difficult to separate the two so as to secure the oxygen for any practical or commercial use. MANUFACTURE OF OXYGEN There are three methods of obtaining oxygen: 1 From _potassium chlorate_, or, as it is commonly called, chlorate of potash. When potassium chlorate (KCLO₃) is heated in a closed vessel (closed vessel means "closed at one end"), it breaks up into potassium chlorid and oxygen; that is, KCLO₃ + heat = KCL + O₃. Potassium chlorate is used in fireworks because it gives up its oxygen readily. Potassium nitrate serves the same purpose in gunpowder, which is a mixture of sulfur (S), charcoal (C), and salt-peter or potassium nitrate (KNO₃). The explosion of gunpowder, after a certain temperature has been reached, is due to the formation of oxygen, which, combined with the potassium nitrate, is set free by the very rapid burning of the charcoal and the sulfur. Other gases formed by the explosion are nitrogen, and probably sulfur dioxid (SO₂), and oxids of nitrogen, N₂O, NO₂, etc. Carbon monoxid and carbon dioxid are sometimes formed. Potassium nitrate, however, is the most active agent in gunpowder. 2 By the _electrolysis of water_. By this method the oxygen and the hydrogen are separated by electricity. 3 By the _liquefaction of air_, which is a very recent and a very scientific method.